The present invention relates to catheters used during interventional and/or diagnostic procedures for delivering fluids into a patient. The present invention particularly relates to an angiographic catheter having controlled fluid flow properties for delivering fluids, such as contrast media, into a human or animal body.
Catheters are commonly used in the diagnosis and treatment of various medical conditions and advancements in catheter designs and materials have made them particularly well-suited for intravascular procedures and intravascular therapies. A conventional catheter includes a small, elongated tube made of flexible, biocompatible materials that enable the catheter to be easily maneuvered through body passages and vascular structures. During an angiographic procedure, the distal end of the catheter is typically inserted into the body via small incisions in the groin area or upper arm and guided through anatomical passages and/or blood vessels to a target site using guide wires and associated imaging techniques. The proximal end is then connected to the device for performing the desired procedure. One such device is an angiographic injector such as the injector disclosed in U.S. patent application Ser. No. 08/957,228 and/or the injector disclosed in U.S. Pat. No. 5,800,397, both of which are commonly assigned to the owner of the present application and both of which are hereby incorporated by reference.
An example of a procedure using a catheter is angiography. Angiography is a procedure used to specifically image, diagnose and treat abnormalities in the heart or vascular structures. During angiography, a physician inserts a catheter and injects contrast material through the catheter into a vein or artery of a patient. The area of the patient""body injected with the contrast material is imaged using x-ray energy or magnetic fields (as used in magnetic resonance imaging) and the resulting image is recorded and/or displayed on a monitor. The images can be used for many purposes, including diagnostic activities as well as interventional procedures such as angioplasty, wherein a balloon is inserted into a vascular system and inflated to open a stenosis.
During the injection procedure, fluid typically flows out of the open distal end of the catheter tip. However, the fluid dynamics associated with some catheter designs often cause the catheter to be pushed back or to recoil as a result of the velocity of the fluid as it exits the distal tip. In effect, the recoil force of the catheter is directly proportional to the fluid velocity at the tip.
Such undesirable recoil movement is particularly acute when using a catheter of small size, e.g. less than about 4 French, since these catheters experience particularly high fluid exit velocities due to the flow requirements in a typical angiographic procedure. However, even larger catheters may be prone to higher recoil if fluid flow out of the tip is of sufficient velocity. Overall, however, smaller angiographic catheters are more prone to severe whipping and recoil at the outset of an injection than catheters of a larger size. This, in part, is due to the structural characteristics of the catheters. In particular, as catheter shaft diameter decreases, the bending force is reduced by the diameter to the third power. Thus, a reduction in shaft diameter from 6 to 4 French gives a four fold reduction in bending force given the same load and distance at which the load is applied.
Catheter designs incorporating valves or openings located along the distal portion of the catheter wall have been considered in an attempt to better facilitate control of the fluid flow. An example of such a device may be found in U.S. Pat. No. 5,250,034, which discloses a pressure responsive valve catheter. The catheter is formed of a relatively non-compliant material, such as nylon, to prevent the sidewalls of the catheter from expanding under the high internal fluid pressures. Slits formed in the catheter wall act as pressure responsive valves to permit fluid to exit the internal lumen of the catheter while preventing material from entering the catheter lumen via the slits. The catheter also includes a distal end hole which may be sealed with an occluding ball located on a guide wire, thereby causing all the fluid to flow from the slits. Alternatively, when the occluding ball is not seated in the end hole, both the fluid and guide-wire may exit from the end hole.
Another example may be found in U.S. Pat. No. 5,807,349, which discloses a catheter having a valve mechanism to permit the infusion or aspiration of fluids between the catheter and the vessel in which the catheter is positioned. The valve is located at the distal end of the catheter and, preferably, is in a plane which is oriented at an angle to the longitudinal axis of the catheter.
The above-described catheters used during angiographic procedures (and other similar devices not specifically described) offer many advantages to control fluid flow. However, it has been discovered that these catheter designs do not adequately address problems with catheter recoil within the vessel or body cavity. Further, these and other state of the art catheter valve mechanisms may still suffer from erratic opening and closing of the valves which can trigger catheter recoil. Furthermore, none of these designs nor any other designs known to the inventors appear to address the particularly acute problem of recoil with small (e.g. less than about 4 French) catheters used in angiography procedures.
In this connection, it is also important to note that there is a continuing need and desire in the medical field to reduce trauma to patients that are undergoing invasive therapies. In the context of catheter placement, this desire has led to a consideration of how to reduce patient trauma during the placement and removal of the interventional catheter.
In current techniques, the catheters that are used require a sizable incision in the patient such that there is considerable pain encountered by the patient and considerable attention to wound control is demanded of the clinician. Indeed, the wound created for such procedures requires the clinician to apply a sizable bandage or other wound containment device (e.g., a product known as Perclose from Percutaneous Vascular Surgery) in order to ensure proper treatment and closure of the wound. Furthermore, such a wound requires significant time in order for proper healing to occur.
As a result, there is an increasing desire to use smaller sized catheters in such interventional therapies so as to make the intervention as minimally invasive as possible. Such small catheters require a significantly smaller incision and thus trauma is reduced and quicker healing is obtained. However, as stated previously, such smaller catheters typically are accompanied with drawbacks such as undesirable flow characteristics (e.g. recoil).
In view of the above, although presently available catheters seem well accepted by the medical community and generally function as required, it is desirable to have a catheter with more controlled fluid flow characteristics and less invasive attributes. In particular, it is desirable to have a small diameter catheter that allows for the management of fluid forces to stabilize the distal tip over a wide range of injection parameters. It is also desirable that there be substantially low or no recoil of the catheter tip in a small diameter catheter during high volume injections, such as those associated with coronary or ventricular angiography. In addition, it is desirable to have a xe2x80x9cuniversalxe2x80x9d catheter that may be used for a variety of surgical procedures and that reduces trauma inflicted on the patient. The concept of a xe2x80x9cuniversalxe2x80x9d catheter, as applied to the present invention, is similar to a muzzle brake device that attaches to the outside barrel of any firearm and functions to reduce recoil of the firearm while maintaining discharge accuracy. Therefore, as with the muzzle brake device, it is desirable that the present invention is adaptable to a variety of catheter designs and reduces catheter movement during various medical procedures.
In view of the foregoing, it is an object of the present invention to provide a catheter assembly that addresses the obstacles and disadvantages associated with the current problem of catheter recoil caused by undesirable fluid forces during an injection procedure.
A further object of the present invention is to provide a small diameter catheter assembly that allows for the management of fluid forces to stabilize the distal tip over a wide range of injection parameters.
A further object of the present invention is to provide a catheter that is less invasive and reduces patient trauma.
These and other objects not specifically enumerated herein are believed to be addressed by the present invention which contemplates a catheter assembly comprising a hub section located at a proximal end of the catheter, a shaft section attached to the distal end of the hub, a stem section that is connected to the distal end of the shaft, and a distal tip section attached to the distal end of the stem section. In addition, the catheter assembly also includes a plurality of openings located in the stem and tip sections that provide proper balancing of fluid forces as the fluid exits the openings of the catheter.
A further object of the present invention is to provide a catheter for use in performing a medical procedure comprising an elongated tubular structure having a proximal end and a distal end. The tubular structure is configured to be a size of no greater than about 4 French and is designed to accommodate fluid flow rates in a range of approximately 0 to 40 ml/sec, and pressures up to 1200 psi, without causing failure of the tubular structure. In addition, the distal end of the catheter includes an elastic restrictor and a plurality of openings arranged such that forces resulting from the fluid flow are substantially balanced during performance of the medical procedure. The elastic restrictor is also configured to allow insertion of a guidewire greater than 0.508 mm in diameter through the distal end of the restrictor.
A further object of the present invention is to provide a method of performing a medical procedure by providing a catheter having a proximal end and a distal end and having a size no greater than about 4 French and introducing the catheter into a patient. The procedure also involves introducing a fluid into the patient at a flow rate in the range of approximately 0 to 40 ml/sec without causing failure to the catheter. Since the flow rate is limited to the maximum pressure allowed based on catheter size, a 4 French catheter will allow for a flow rate of 15 ml/sec maximum at 1200 psi. A final objective of the method includes balancing forces acting on the catheter resulting from the introduction of fluid flow by variably restricting the fluid flow at the distal end of the catheter according to the flow rate and by directing fluid out of a plurality of openings in a wall of the catheter.
A further object of the present invention is to provide a fixture for measuring catheter movement during a simulated injection procedure. The fixture comprises a plurality of walls forming at least one chamber. A first wall of the fixture includes one or more openings sized to hold a catheter. The fixture also includes a second wall including a grid such that catheter movement can be calculated and scaled against the grid.
A further object of the present invention is to provide a method of measuring catheter movement during a simulated injection procedure. The method includes filling a chamber of a test fixture with fluid and suspending a catheter from the fixture. The method also includes flowing an amount of a fluid at a controlled flow rate through the catheter and measuring catheter movement against a grid on the test fixture.
A further object of the present invention is to provide a fixture for measuring fluid backflow from a catheter during a simulated injection procedure. The fixture comprises a plurality of walls forming a first chamber and a second chamber, wherein the first chamber and the second chamber are filled with a fluid. The fixture also includes a first wall having one or more openings sized to hold a catheter and a second wall separating the first chamber and the second chamber. The second wall includes an opening such that an amount of dyed fluid flowing from the catheter into the first chamber and the second chamber can be measured based on a visual comparison and rating of dye density between the first chamber and the second chamber.
A further object of the present invention is to provide a method of measuring fluid backflow from a catheter during a simulated injection procedure. The method includes filling a first chamber and a second chamber of a test fixture with fluid and suspending a catheter from the fixture. Further, the method includes positioning the catheter in an opening of a wall separating the first chamber from the second chamber and flowing an amount of a dyed fluid at a controlled flow rate through the catheter. The amount of fluid backflow is then determined by visually comparing and rating dye density between the first chamber and the second chamber.